This is because you have too much content in the Hero banner. The Hero banner will always be the size of the display. That is what the Hero feature is essentially.
In your case it would be better to simply turn off the Hero feature and use a Fluid banner height, allowing the banner to expand to the size of your content.
Honestly, I would say a Fluid banner height is the right choice 90% of the time when it comes to responsive design. It is just a better choice for most content.